Computer991

Hi guys I'm fairly new to eletronics and what not so I'm not too sure whats the best really... I'm planning on making a pretty big LED wall but I'm not too sure what to use I've seen a ton of video of people using the WS2801 but it's quite expensive the cheapest I've found is 50 for 20USDI've also heard great things about the 74HC595 and it is quite cheaper 100 for 20 USDso my question is Which one is better for a big LED wall?

the WS2801 can sink twice as much current, and it supports pwm meaning you can set the brightness of each LED if you wanted more than full on full off operation, but it appears to be in surface mount only so you will either have to make a board (not that hard) or cut some pads in half on a perforated board and solder wires, which is also not that hard, but fiddly.

http://www.futurlec.com/Others/WS2801pr.shtml

(29 bucks for 100 aint bad)

or buy that little breakout board they have next to it on the page above

The 74HC595 is a general-purpose logic device (not specifically for LEDs). It has 8 outputs (for 8 LEDs), but it doesn't have built-in current limiting so you need a current-limiting resistor for each LED. (You can get "resistor packs" with 8 resistors in one "device".

The WS2801 is a special-purpose LED driver chip. It has 3 outputs for 3 LEDs or for one RGB (multi-color) LED. It also has built-in current-limiting and built-in dimming features.

I can't tell you not to consider cost... But, it's usually better to look for the best or easiest solution rather than the cheapest solution, especially when you are building a one-off gizmo. If you are building & selling hundreds or thousands of an item it becomes really important to minimize cost.

Just to complicate things more for you... Maxim makes several constant-current LED drivers with up to 16 outputs. But, I think they are more costly than what you're considering. I'm using 6 of Maxim's 8-port LED drivers in my current project to drive 48 LEDs.

Computer991

Wow thank you for that link I already bought 50 for 20 usd and it was free shipping but on my next buy (Which i probly will need more) I will buy some from these.Another question

Do you guys know any places where I can find good schematics examples for the WS2801? I'm not too sure how I should go about wiring I don't want to mess anything up.I've seen this example and it looks great but What resistors are they using and what other chips are on there? http://learn.adafruit.com/system/assets/assets/000/001/138/original/36mm-io.jpg?1342657099

Yeah I've seen some of maxims stuff its really nice but so expensive D:

The datasheet has all the info you need, though comprehending datasheets is something that just comes with time and meddling with stuff

http://www.futurlec.com/Others/WS2801.shtml

This is a RGB driver, so what you have is one per LED (and in turn there are 3 LED's per package), if your using just one color LED well ... you have a chip that can drive 3 LED's, if thats the case ignore the whole RGB on the sheet.

Page 2 is what I call the death page, it shows you min and MAX ratings of the part, its best to stick near typical, and never exceed max ... in fact dont get within 10% of max.

If you scroll to page 5, you will see how to chain them

Page 8 shows you an example using the part to modulate a high voltage side, ie if you wanted to some rebels at 12 volts pushing 300ma, which one will leave you color blind for a second, hate to imagine a large wall of them...

Page 9 shows you an example if your LED's exceed the current ratings of the part (50ma per channel max)

12 shows you an example of clock vs data so you can program it .. if there is not a library already (and if there is not, theres plenty of help here)

and page 15 shows there is a though hole DIP package, but f if I know where to fine one heh

I think your biggest issue is going to be finding a power supply for a wall-o-LED's, and maybe speed depending on row * column * *colordepth (or grey scale) counts

Quote

Yeah I've seen some of maxims stuff its really nice but so expensive D:

OMG yea maxim is expensive, I recently went out to find MAX232 chips, they convert normal RS232 serial signals to inverted TTL serial signals that are micro happy, at digikey for the maxim part is 3.76$ EACH, the totally compatible, slightly better performing Texas Insturments clone .... 85 cents each

Computer991

Thanks for the reply I was reading through the datasheet and as a newbie to electronics I have no clue what most of it ment but thank you for clearing some of it up, ill definite print this up and give it a good read.

Also @ Crossroads wow those chips are awesome I really wish I had seen those earlier they are great for the price...Ill try to use them on my next run quick question tho are they compatible with the WS2801 or would I have to use different systems for the chips?

dhenry

A big plus for hc595 is the output latch: it allows the display to be updated once, thus no flickering. Not to mention its wide availability. But you cannot (practically) manage grayscale for individual bits - you can manage the grayscale for all bits, however.

A big plus for ws280x is the ability to manage grayscale for individual bits. However, their output is transparent so the display gets updated as the data is piped in. Not to mention the gap time between each frame.

So if you need to drive individual leds differently (uneven leds for example), go with ws280x (the issue for large number of leds driven by ws280x is the long transfer time -> flickering). Otherwise, hc595 is a better choice.

Another option - use MAX7219, can drive 64 LEDs. All will have the same 31 level of intensity control. It does the multiplexing at 800 Hz, no flickering. Update with SPI transfers, nice & fast. 4 chips driving 256 LEDs, make them the high brightness kind, light up your room pretty nice!